Automated machine tool systems require a precise means of locating surfaces on workpieces. One of the most common methods of accomplishing this task is to have the machine move a probe into contact with the workpiece and to record the probe position when contact is made. Probes of this type are known as touch probes. They generally include a stylus for contacting the workpiece and circuitry which operates to generate an electrical signal when the stylus contacts the part. A machine controller can calculate information about the shape or location of the part from the X, Y and Z axes positional data of the probe when the stylus contact generates the electrical signal. Probes of this general configuration have also been used to perform dimensional gauging operations where the displacement of the stylus is used to provide gauging information.
The patent literature discloses several probe designs which are adapted to be used in automatic machining centers where the probes are temporarily stored in a tool magazine and are connected and removed from the spindle by an automatic tool changer mechanism. Representative examples of this general type are disclosed in U.S. Pat. No. 4,339,714 to Ellis; U.S. Pat. No. 4,118,871 to Kirkham; U.S. Pat. No. 4,328,623 to Juengel et al; U.S. Pat. No. 4,153,998 to McMurtry; and U.S. Ser. No. 259,257 entitled "Apparatus for Detecting the Position of a Probe Relative to a Workpiece", filed Apr. 30, 1981 by Juengel (now U.S. Pat. No. 4,401,945) which is assigned to the assignee of this invention.
In general, the probe assemblies include a main body or housing in which an end thereof opposite the stylus is connected to a suitable adapter. The adapter allows the probe housing to be incorporated into an automated machine tool in the same way as a typical cutting tool. The adapters vary in configuration depending upon the machine tool in which the probe is to be utilized. The adapters can also be configured to enable the probe to be used with a hand or gripping element of an automaton, such as an industrial robot.
It is important that the proper location and orientation of the stylus be provided in order for the probe to generate accurate data. For example, it is often imperative that the tip of the stylus and its associated shaft be precisely centered with the axis of the spindle drive when the probe is used in a machining center. In the past, such precision was attempted to be achieved by maintaining strict tolerances or using special procedures during the construction of the probe. However, such precautions were not always adequate and, in any event, they increased the manufacturing costs of the probe assembly.